1. Field of the Invention
This invention relates to locking devices and more particularly is a locking device adapted for attachment to a fire hydrant to inhibit unauthorized operation of the hydrant.
2. Prior Art
Locking devices to prevent unauthorized operation of fire hydrants are well known and have been in use for a number of years.
A first example of a fire hydrant locking device is disclosed in U.S. Pat. No. 3,556,131. The device includes a dome-shaped upper element formed with an inner recess. This inner recess is divided into an upper, small diameter portion and a lower, larger diameter threaded portion. Fitting in the dome element upper portion recess is an upper, large cylindrical part of an actuating nut element. This actuating nut element is formed with an inner opening and three radially spaced apart threaded bores for set screws to secure the nut element to an actuating nut of the hydrant. The nut element further includes a lower, small diameter cylindrical part that forms an offset for a ring-shaped element. This ring element has peripheral external threads to interconnect with the dome element internal threads. At attached, the cap and ring element are free to rotate with respect to the actuating nut element. As the locking device is positioned on the hydrant nut, a gap between a top of the hydrant and a bottom of the locking device allows insertion of the tool to rotate the hydrant actuating nut.
An example of a fire hydrant that includes tamper proof structure is set out in U.S. Pat. No. 4,566,481. In this case, an actuating nut of the hydrant is formed with a horizontally positioned annular groove. Positioned in this groove are inner portions of two C-clips. Outer portions of these C-clips then are located in a space defined by an upper annular recess in a lower retaining portion and a bottom annular surface of a dome-shaped cap member. In a lower surface of the retaining portion is a pair of oppositely positioned downward facing holes. The cap member and lower retaining portion are threadedly joined. As the assembled retaining portion and cap are positioned on the hydrant actuating nut, a small gap between a top closure member of the hydrant and the lower surface of the retaining portion allows insertion of operative ends of a flat wrench. This wrench has pins that fit into the retaining portion holes to allow the wrench to rotate the operatively connected hydrant actuating nut.
Another example of a fire hydrant that includes actuating nut tamper proof structure is disclosed in U.S. Pat. No. 4,936,336. This structure includes a shroud, a cap, and an actuating body that fits inside the shroud and extends upward into the cap. This actuating body is formed with a polygonal-shaped recess that fits over an actuating nut of the hydrant. The actuating body is secured to the hydrant nut by a set of sets screws operatively carried in threaded bores in the actuating body. The shroud is secured to the actuating body by a snap ring positioned in aligning annular grooves in a sidewall of the actuating body and in a sidewall of an inner cylindrical recess of the shroud. Access to these set screws is provided by a threaded bore in the shroud sidewall that is sealable by a plug having a selective curvilinear grooved outer face. The cap is joined to an upper portion of the actuating body by a second snap ring positioned in respective aligning annular grooves inside the cap and in a sidewall of the actuating body. As the cap is located, there is a narrow gap between a bottom edge of the cap and a top edge of the shroud. This gap allows insertion of a head of a wrench to rotate the actuating body that in turn rotates the hydrant actuating nut.
Lastly, U.S. Pat. No. 5,205,312 sets out a fire hydrant locking arrangement that includes an inner cylindrical member that fits inside an outer cylindrical member. An outer cylindrical wall surface of the inner member and inner cylindrical wall surface of the outer member are formed with respective aligning circumferential groove portions. These groove portions connect with aligning bores in sidewalls of the inner and outer members that allow insertion of an end of a ductile, low melting temperature metal rod. Rotation of the outer cylindrical portion pulls the rod through the outer portion bore to fill the groove portions and form a 360 degree locking ring. To gain access to the inner cylindrical member and operatively joined hydrant actuating nut, the structure is heated to 1,466 degrees F. to melt the locking ring.
Further fire hydrant locking devices and hydrant tamper proof structure are set out in U.S. Pat. Nos. 4,526,193, 4,825,898, 5,630,442, 5,632,301, 5,722,450, and 5,727,590.